1. Field of the Invention
This invention relates to an optical device such as lens barrels used in image pickup devices, and more particularly to a support mechanism for supporting the optical device.
2. Prior Art
Conventionally, an image pickup device has been proposed which is provided with a zoom mechanism having lens barrels composed of a fixed barrel rigidly fixed to the body of the image pickup device and having a cam groove formed in an inner peripheral surface thereof, and a moving cam ring fitted in the cam groove, wherein the moving cam ring is driven for rotation by a motor so as to move a zoom lens.
In the image pickup device of this kind, the moving cam ring is supportedly fitted in the cam groove of the fixed barrel only by means of three followers formed with tapers.
Therefore, when an external force, e.g. an impact, is applied to the lens barrel in an extended position, there is a fear that the moving cam ring becomes disengaged from the cam groove of the fixed barrel.
One way to solve this problem may be to employ a method of using followers with no tapers for supporting the moving cam ring in the fixed barrel. This method, however, has the disadvantage that the lens barrel can be broken, although disengagement of the moving cam ring can be prevented. Further, another problem may arise, that is, the moving cam ring cannot be centered.
The present invention has been made in view of the above problems, and an object thereof is to provide an optical device which is free from disengagement of coupling elements of a coupling mechanism for moving an optical unit even if an external force, such as an impact, is applied to the optical device.
To attain the above object, the present invention provides an optical device comprising a first barrel, a second barrel that is shifted relative to the first barrel for moving an optical unit, the second barrel being fitted to the first barrel, and first and second engaging portions which can be engaged with each other when the second barrel is in a predetermined positional relationship with respect to the first barrel, the first and second engaging portions preventing the second barrel from being disengaged from the first barrel and displaced in a direction along an optical axis relative to the first barrel.
Preferably, the first barrel comprises a fixed barrel.
More preferably, the second barrel comprises a moving cam ring.
Preferably, the first and second engaging portions comprise protrusions which cane be engaged with each other.
Preferably, the first and second engaging portions are provided on the first barrel and the second barrel, respectively.
Preferably, the second barrel is brought into the predetermined positional relationship with respect to the first barrel, when the second barrel is shifted forward relative to the first barrel.
More preferably, when the second barrel is in the predetermined positional relationship with respect to the first barrel, the second engaging portion is positioned in front of the first engaging portion.
Preferably, the optical device comprises a lens barrel.
Preferably, the optical device comprises an image pickup device.
The above and other objects, features, and advantages of the invention will become more apparent from the following detailed description taken in conjunction with the accompanying drawings.